• Photosynthesis
– Occurs in plants, algae, certain other protists, and some prokaryotes
These organisms use light energy to drive the synthesis of organic molecules from carbon dioxide and (in most cases) water. They feed not only themselves, but the entire living world. (a) On land, plants are the predominant producers of food. In aquatic environments, photosynthetic organisms include (b) multicellular algae, such as this kelp; (c) some unicellular protists, such as Euglena; (d) the prokaryotes called cyanobacteria; and (e) other photosynthetic prokaryotes, such as these purple sulfur (a) Plants bacteria, which produce sulfur (spherical globules) (c, d, e: LMs).

• The absorption spectra of three types of pigments in chloroplasts
Three different experiments helped reveal which wavelengths of light are photosynthetically important. The results are shown below.
EXPERIMENT

• The action spectrum for photosynthesis
– Was first demonstrated by Theodor W. Engelmann
Aerobic bacteria
Filament of alga

500 600 700 400 (c) Engelmann‘s experiment. In 1883, Theodor W. Engelmann illuminated a filamentous alga with light that had
been passed through a prism, exposing different segments of the alga to different wavelengths. He used aerobic bacteria, which concentrate near an oxygen source, to determine which segments of the alga were releasing the most O2 and thus photosynthesizing most. Bacteria congregated in greatest numbers around the parts of the alga illuminated with violet-blue or red light. Notice the close match of the bacterial distribution to the action spectrum in part b.

CONCLUSION
photosynthesis.

Light in the violet-blue and red portions of the spectrum are most effective in driving

A Comparison of Chemiosmosis in Chloroplasts and Mitochondria • Chloroplasts and mitochondria
– Generate ATP by the same basic mechanism: chemiosmosis – But use different sources of energy to accomplish this